Puerto Rican coqui frogs were accidentally introduced to Hawaii in the 1980s, and today there are as many as 91,000 frogs per hectare in some locations. What does that mean for native wildlife? Concerns that ravenous coquis could reduce the food available for the islands' native insect-eating birds, many of which are already declining, spurred researchers to examine the relationship between frog and bird populations -- but their results weren't what they expected.